I tried using Krita several times, mostly because of its animation features, to replace my current GIMP + a custom set of animation plugins setup. But it's always unbearably slow on my computer for some reason. By slow I mean lag when updating the canvas - there's a very noticeable delay between moving the stylus with my hand (I'm using a Wacom Cintiq) and when the line appears on the screen.

It's probably something specific about my hardware and/or Debian system (I've been trying Krita's AppImage downloads). GIMP on the other hand doesn't have any problems with it.

Are you using a very large or computationally intensive brush, by chance? Krita has a fairly tweakable brush engine which is also easy to abuse.

Are the default brushes computationally expensive? I've never got far enough with Krita to play with custom brushes.

I like Krita a lot. It might be the best not-Photoshop on Linux. I just wish I could choose a default tool when I open up an image, rather than it defaulting to the brush...

Sounds like a feature request to me: https://bugs.kde.org/